package jmind.core.concurrent;

/**
CountDownLatch类是一个同步计数器,构造时传入int参数,该参数就是计数器的初始值，每调用一次countDown()方法，计数器减1,计数器大于0 时，await()方法会阻塞程序继续执行
CountDownLatch如其所写，是一个倒计数的锁存器，当计数减至0时触发特定的事件。利用这种特性，可以让主线程等待子线程的结束。下面以一个模拟运动员比赛的例子加以说明。
*/
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CountDownLatchDemo {
    private static final int PLAYER_AMOUNT = 5;

    public CountDownLatchDemo() {
        // TODO Auto-generated constructor stub    
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        //对于每位运动员，CountDownLatch减1后即结束比赛
        CountDownLatch begin = new CountDownLatch(1);
        //对于整个比赛，所有运动员结束后才算结束
        CountDownLatch end = new CountDownLatch(PLAYER_AMOUNT);
        Player[] plays = new Player[PLAYER_AMOUNT];

        for (int i = 0; i < PLAYER_AMOUNT; i++)
            plays[i] = new Player(i + 1, begin, end);

        //设置特定的线程池，大小为5
        ExecutorService exe = Executors.newFixedThreadPool(PLAYER_AMOUNT);
        for (Player p : plays)
            exe.execute(p); //分配线程
        System.out.println("Race begins!");
        begin.countDown();
        try {
            end.await(); //等待end状态变为0，即为比赛结束
        } catch (InterruptedException e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            System.out.println("Race ends!");
        }
        exe.shutdown();
    }

}

class Player implements Runnable {

    private int id;
    private CountDownLatch begin;
    private CountDownLatch end;

    public Player(int i, CountDownLatch begin, CountDownLatch end) {
        // TODO Auto-generated constructor stub
        super();
        this.id = i;
        this.begin = begin;
        this.end = end;
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub
        try {
            begin.await(); //等待begin的状态为0
            Thread.sleep((long) (Math.random() * 100)); //随机分配时间，即运动员完成时间
            System.out.println("Play" + id + " arrived.");
        } catch (InterruptedException e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            end.countDown(); //使end状态减1，最终减至0
        }
    }
}